Neutral particle beam processing apparatus

ABSTRACT

A neutral particle beam processing apparatus comprises a workpiece holder ( 20 ) for holding a workpiece (X), a plasma generator for generating a plasma in a vacuum chamber ( 3 ), an orifice electrode ( 5 ) disposed between the workpiece holder ( 20 ) and the plasma generator, and a grid electrode ( 4 ) disposed upstream of the orifice electrode ( 5 ) in the vacuum chamber ( 3 ). The orifice electrode ( 5 ) has orifices ( 5   a ) defined therein. The neutral particle beam processing apparatus further comprises a voltage applying unit for applying a voltage between the orifice electrode ( 5 ) and the grid electrode ( 4 ) via a dielectric ( 5   b ) to extract positive ions from the plasma generated by the plasma generator and pass the extracted positive ions through the orifices ( 5   a ) in the orifice electrode ( 5 ).

TECHNICAL FIELD

The present invention relates to a neutral particle beam processingapparatus, and more particularly to a neutral particle beam processingapparatus for generating a highly directional and highly dense neutralparticle beam from a high-density plasma and processing a workpiece withthe generated neutral particle beam.

BACKGROUND ART

In recent years, semiconductor integrated circuits, information storagemedia such as hard disks, micromachines, and the like have beenprocessed in highly fine patterns. In the fields of processing suchworkpieces, attention has been attracted to the use of an energetic beamsuch as a high-density ion beam which is highly linear, i.e., highlydirectional, and has a relatively large beam diameter. For example, theenergetic beam is applied to a workpiece for depositing a film thereonor etching the workpiece.

As beam sources of such energetic beams, there have been used beamgenerators which generate various kinds of beams including a positiveion beam, a negative ion beam, and a radical beam. The positive ionbeam, the negative ion beam, or the radical beam is applied to a desiredarea of a workpiece from the beam source, for thereby locally depositinga film on the workpiece, etching the workpiece, modifying the surface ofthe workpiece, or joining or bonding parts of the workpiece.

In the case of a beam source which applies charged particles such aspositive ions or negative ions to a workpiece, an insulated workpiececannot be processed because of a charge build-up phenomenon in whichelectric charges are built up on the workpiece. Further, since the ionbeam emitted from the beam source tends to spread due to thespace-charge effect, the workpiece cannot be processed in a finepattern.

In order to solve the above problems, there has been proposed a methodof introducing electrons into the ion beam to neutralize the electriccharges. This method can balance the electric charges on the workpieceon the whole. However, since local unbalance of the electric chargesstill remains on the workpiece, the workpiece cannot be processed in afine pattern.

In the case where ions are extracted from a plasma source and applied toa workpiece, if radiation (e.g., an ultraviolet ray) produced by theplasma source is applied to the workpiece, then the radiation adverselyaffects the workpiece. Thus, it is necessary to shield the workpiecefrom adverse radiation (e.g., an ultraviolet ray) emitted from theplasma source.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above drawbacks. Itis therefore an object of the present invention to provide a neutralparticle beam processing apparatus which can apply an energetic beamhaving a large beam diameter to a workpiece with an inexpensive andcompact structure, and can neutralize ions with a high neutralizationefficiency to process the workpiece without a charge build-up or damage.

According to a first aspect of the present invention, there is provideda neutral particle beam processing apparatus comprising: a workpieceholder for holding a workpiece; a plasma generator for generating aplasma in a vacuum chamber; an orifice electrode disposed between theworkpiece holder and the plasma generator, the orifice electrode havingorifices defined therein; a grid electrode disposed upstream of theorifice electrode in the vacuum chamber; and a voltage applying unit forapplying a voltage between the orifice electrode and the grid electrodevia a dielectric to extract positive ions from the plasma generated bythe plasma generator and pass the extracted positive ions through theorifices in the orifice electrode.

With the above arrangement, since the workpiece can be processed by aneutral particle beam having no electric charges but having a largetranslational energy, various processes including an etching process anda deposition process can be performed on the workpiece with highaccuracy in such a state that an amount of charge build-up is reduced.Particularly, when the orifice electrode is used for neutralizing thenegative ions, a high neutralization efficiency can be obtained, andhence a beam diameter of an energetic beam can be increasedinexpensively without increasing the size of the apparatus. Further,since the generated plasma is isolated from the workpiece by the orificeelectrode, a radiation produced by the plasma is not substantiallyapplied to the workpiece. Therefore, it is possible to reduce adverseeffects on the workpiece due to the radiation such as an ultraviolet raywhich would otherwise damage the workpiece.

According to a second aspect of the present invention, there is provideda neutral particle beam processing apparatus comprising: a workpieceholder for holding a workpiece; a plasma generator for generating aplasma in a vacuum chamber; an orifice electrode disposed between theworkpiece holder and the plasma generator, the orifice electrode havingorifices defined therein; a grid electrode disposed upstream of theorifice electrode in the vacuum chamber; and a voltage applying unit forapplying a high-frequency voltage between the orifice electrode and thegrid electrode via a dielectric to generate a plasma between the orificeelectrode and the grid electrode and to extract positive ions from thegenerated plasma and pass the extracted positive ions through theorifices in the orifice electrode.

With the above arrangement, the orifice electrode serves not only toneutralize the positive ions, but also to generate the plasma.Therefore, a high neutralization efficiency can be obtained by theorifice electrode, and simultaneously it is not necessary to provide aseparate plasma generator for generating a plasma. Thus, the neutralparticle beam processing apparatus can be made compact in structure, anda beam diameter of an energetic beam can be increased inexpensively.

According to a preferred aspect of the present invention, the dielectriccomprises a dielectric film covering a surface of the orifice electrode.When the surface of the orifice electrode is covered with a dielectricfilm, more electrons are charged on the dielectric film with weakbonding energies than usual. Therefore, the positive ions that arepassing through the orifices have a higher probability of recombinationwith the electrons. Accordingly, the neutralization efficiency ofpositive ions can further be enhanced.

The above and other objects, features, and advantages of the presentinvention will be apparent from the following description when taken inconjunction with the accompanying drawings which illustrates preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a whole arrangement of a neutralparticle beam processing apparatus according to a first embodiment ofthe present invention;

FIG. 2A is a perspective view showing an orifice electrode in theneutral particle beam processing apparatus shown in FIG. 1;

FIG. 2B is a vertical cross-sectional view partially showing the orificeelectrode shown in FIG. 2A;

FIG. 3 is a graph showing the potential of a plasma and the potential ofthe orifice electrode in the first embodiment of the present invention;

FIG. 4 is a schematic view showing a whole arrangement of a neutralparticle beam processing apparatus according to a second embodiment ofthe present invention;

FIG. 5 is a timing chart showing operating states of the neutralparticle beam processing apparatus shown in FIG. 4; and

FIG. 6 is a timing chart showing an example of a voltage to be appliedinstead of a low-frequency voltage.

BEST MODE FOR CARRYING OUT THE INVENTION

A neutral particle beam processing apparatus according to a firstembodiment of the present invention will be described in detail belowwith reference to FIGS. 1 through 3.

FIG. 1 is a schematic view showing a whole arrangement of a neutralparticle beam processing apparatus according to a first embodiment ofthe present invention, with electric components in block form. As shownin FIG. 1, the neutral particle beam processing apparatus comprises acylindrical vacuum chamber 3 constituted by a beam generating chamber 1for generating a neutral particle beam and a process chamber 2 forprocessing a workpiece X such as a semiconductor substrate, a glassworkpiece, an organic workpiece, a ceramic workpiece, or the like. Thevacuum chamber 3 is a metallic chamber, which is made of metal, and athin-plate grid electrode 4 made of an electrically conductive materialis disposed in an upstream end of the vacuum chamber 3. The vacuumchamber 3 and the grid electrode 4 are electrically connected to eachother and electrically grounded. The grid electrode 4 may comprise ameshed wire, a punching metal, or the like.

The beam generating chamber 1 has a gas inlet port 11 defined in anupper portion thereof for introducing a gas into the beam generatingchamber 1. The gas inlet port 11 is connected through a gas supply pipe12 to a gas supply source 13, which supplies a gas such as SF₆, CHF₃,CF₄, Cl₂, Ar, O₂, N₂, and C₄F₈ to the beam generating chamber 1.

The process chamber 2 houses a workpiece holder 20 therein for holding aworkpiece X. The workpiece X is placed on an upper surface of theworkpiece holder 20. The process chamber 2 has a gas outlet port 21defined in a sidewall thereof for discharging the gas from the processchamber 2. The gas outlet port 21 is connected through a gas outlet pipe22 to a vacuum pump 23, which operates to maintain the process chamber 2at a predetermined pressure.

An orifice plate (orifice electrode) 5 made of an electricallyconductive material such as aluminum is disposed in the lower end of thebeam generating chamber 1. The orifice electrode 5 is electricallyconnected to an AC power supply (voltage applying unit) 100. The vacuumchamber 3 and the orifice electrode 5 are electrically insulated fromeach other by an insulating material (not shown).

FIG. 2A is a perspective view showing the orifice electrode 5, and FIG.2B is a vertical cross-sectional view partially showing the orificeelectrode 5 shown in FIG. 2A. As shown in FIGS. 2A and 2B, the orificeelectrode 5 has a number of orifices 5 a defined therein. As shown inFIG. 2B, the surfaces of the orifice electrode 5 are covered withdielectric films 5 b. The dielectric films 5 b may comprise aluminumoxide films. Alternatively, the dielectric films 5 b may comprisenitride films or oxide films which are formed on a silicon material ordielectric films spray-coated on an electrically conductive material.

Operation of the neutral particle beam processing apparatus according tothe first embodiment will be described below. FIG. 3 is a graph showingthe potential of the plasma and the potential of the orifice electrode 5in the present embodiment. In FIG. 3, T represents the period of thepotentials.

The vacuum pump 23 is driven to evacuate the vacuum chamber 3, and thena gas such as SF₆, CHF₃, CF₄, Cl₂, Ar, O₂, N₂, or C₄F₈ is introducedfrom the gas supply source 13 into the beam generating chamber 1. Ahigh-frequency voltage having a frequency of about 13.56 MHz is appliedto the orifice electrode 5, so that a high-frequency electric field isproduced in the beam generating chamber 1. The gas introduced into thebeam generating chamber 1 is ionized by electrons that are acceleratedby the high-frequency electric field, for thereby generating ahigh-density plasma in the beam generating chamber 1. The plasma ismainly composed of positive ions and heated electrons.

At this time, since the electrons, which move 1000 times faster than theions, reach a cathode earlier than the ions to negatively charge thecathode. This potential attracts the positive ions to the cathode. Sincethe orifice electrode 5 is electrically insulated by the dielectricfilms 5 b, the surfaces of the dielectric films 5 b of the orificeelectrode 5 are charged with the electrons. Therefore, after severalcycles of the high-frequency electric field, a steady state isestablished to prevent electrons from excessively passing through theorifice electrode 5. Thus, a sheath is formed upstream of the orificeelectrode 5. The positive ions are accelerated by an average potential(self-bias) of the sheath.

Then, the positive ions 6 (see FIG. 2B) accelerated by the sheath areintroduced into the orifices 5 a defined in the orifice electrode 5.Most of the positive ions 6 that are passing through the orifices 5 a inthe orifice electrode 5 are collided with the sidewall surfaces of theorifices 5 a and hence neutralized in the vicinity of solid sidewallsurfaces of the orifices 5 a, or are collided with gas moleculesremaining within the orifices 5 a and hence neutralized by chargeexchange with the gas molecules, or are collided with electrons chargedon the dielectric films 5 b of the orifice electrode 5 and henceneutralized by recombination with the electrons. Thus, the positive ions6 are converted into neutral particles 7 (see FIG. 2B). Since thedielectric films 5 b are formed on the orifice electrode 5, moreelectrons are charged on the dielectric films 5 b than usual. Therefore,the positive ions 6 that are passing through the orifices 5 a have ahigher probability of recombination with the electrons. Accordingly, aneutralization efficiency of positive ions can be enhanced.

The positive ions 6 that have been neutralized when passing through theorifices 5 a, i.e., the neutral particles 7, are then emitted as anenergetic beam into the process chamber 2. The neutral particles 7travel directly in the process chamber 2 and are applied to theworkpiece X placed on the workpiece holder 20, for thereby etching thesurface of the workpiece X, cleaning the surface of the workpiece X,modifying (e.g., nitriding or oxidizing) the surface of the workpiece X,or depositing a film on the workpiece X.

The orifice electrode 5 serves not only to neutralize the positive ions,but also to prevent a radiation produced by the plasma from beingapplied to the workpiece X. Specifically, since the beam generatingchamber 1 where the plasma is generated is isolated from the workpiece Xby the orifice electrode 5, the radiation produced by the plasma is notsubstantially applied to the workpiece X. Therefore, it is possible toreduce adverse effects on the workpiece X due to the radiation such asan ultraviolet ray which would otherwise damage the workpiece X.

As well known in the art, when an insulated workpiece such as aworkpiece made of glass or ceramics is processed, charge build-up may bedeveloped on the surface of the insulated workpiece. However, byapplying neutralized particles to the insulating workpiece as describedabove, various processes including an etching process and a depositionprocess can be performed on the insulating workpiece with high accuracyin such a state that an amount of charge build-up is reduced. Varioustypes of gases may be introduced into the beam generating chamber 1according to the type of process to be performed on the workpiece X. Forexample, in a dry etching process, oxygen or a halogen gas mayselectively be used according to the kind of the workpiece X.

A neutral particle beam processing apparatus according to a secondembodiment of the present invention will be described below withreference to FIGS. 4 and 5. FIG. 4 is a schematic view showing a wholearrangement of a neutral particle beam processing apparatus according toa second embodiment of the present invention, with electric componentsin block form. In FIG. 4, like parts and components are denoted by thesame reference numerals and characters as those of the first embodimentand will not be described below.

While the vacuum chamber is a metallic chamber in the first embodiment,a vacuum chamber in the second embodiment comprises a beam generatingchamber 1 having walls made of quartz glass or ceramics, and a processchamber 2 having walls made of metal. The beam generating chamber 1 hasa coil 10 disposed therearound for inductively coupled plasma (ICP). Thecoil 10 is housed in a water-cooled tube having an outside diameter of 8mm, for example. The coil 10 of about two turns is wound around the beamgenerating chamber 1. The coil 10 is electrically connected to ahigh-frequency power supply 102, which applies a high-frequency voltagehaving a frequency of about 13.56 MHz, for example, to the coil 10. Whena high-frequency current is supplied from the high-frequency powersupply 102 to the coil 10, an induced magnetic field is produced in thebeam generating chamber 1 by the coil 10. The varying magnetic fieldinduces an electric field. The electric field accelerates electrons,which ionizes atoms and molecules in a gas to generate a plasma in thebeam generating chamber 1. Thus, the coil 10 and the high-frequencypower supply 102 constitute a plasma generator for generating a plasmain the beam generating chamber 1.

The orifice electrode 5 is electrically connected to a low-frequencypower supply (voltage applying unit) 103, which applies a low-frequencyvoltage having a frequency of about 400 kHz, for example, to the orificeelectrode 5. A thin-plate grid electrode 40 made of an electricallyconductive material is disposed upstream of the coil 10 and electricallygrounded.

Operation of the neutral particle beam processing apparatus according tothe second embodiment will be described below. FIG. 5 is a timing chartshowing operating states of the neutral particle beam processingapparatus shown in FIG. 4. In FIG. 5, Va represents the potential of thecoil 10, and Vb represents the potential of the orifice electrode 5. Thetiming chart is schematically shown in FIG. 5, and the shown frequenciesare different from the actual frequencies, for example.

The vacuum pump 23 is driven to evacuate the vacuum chamber 3, and thena gas is introduced from the gas supply source 13 into the beamgenerating chamber 1. As shown in FIG. 5, a high-frequency voltagehaving a frequency of about 13.56 MHz is applied to the coil 10 by thehigh-frequency power supply 102, so that a high-frequency electric fieldis produced in the beam generating chamber 1. The gas introduced intothe beam generating chamber 1 is ionized by electrons that areaccelerated by the high-frequency electric field, for thereby generatinga high-density plasma in the beam generating chamber 1.

At the same time when the high-frequency voltage is applied by thehigh-frequency power supply 102, a low-frequency voltage having afrequency of about 400 kHz is applied between the grid electrode 40 andthe orifice electrode 5 by the low-frequency power supply 103. When apositive voltage is applied to the orifice electrode 5 (for example,during a period “A” illustrated in FIG. 5), electrons in the generatedplasma is attracted to the orifice electrode 5 to charge the surfaces ofthe orifice electrode 5 with the electrons. When a negative voltage isapplied to the orifice electrode 5 (for example, during a period “B”illustrated in FIG. 5), positive ions in the generated plasma isattracted to the orifice electrode 5 and pass through the orifice 5 adefined in the orifice electrode 5. Most of the positive ions that arepassing through the orifices 5 a are neutralized and converted intoneutral particles as in the case of the first embodiment. The neutralparticles are then emitted as an energetic beam into the process chamber2. The neutral particles travel directly in the process chamber 2 andare applied to the workpiece X placed on the workpiece holder 20.

In the present embodiment, the plasma is generated with use of a coilfor ICP. However, the plasma may be generated with use of an electroncyclotron resonance source (ECR source), a coil for helicon wave plasma,a microwave, or the like. The frequency of the high-frequency voltage isnot limited to 13.56 MHz, but may be in the range from 1 MHz to 20 GHz.Further, the frequency of the high-frequency voltage is not limited to400 kHz. For example, a voltage of a rectangular wave as shown in FIG. 6may be applied instead of the low-frequency voltage.

In the above embodiments, the dielectric films are formed on the orificeelectrode. As a dielectric, a blocking capacitor may be inserted betweenthe AC power supply 100 and the orifice electrode 5 in FIG. 1 or betweenthe low-frequency power supply 103 and the orifice electrode 5 in FIG.4.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

INDUSTRIAL APPLICABILITY

The present invention is suitable for use in a neutral particle beamprocessing apparatus for generating a highly directional and highlydense neutral particle beam from a high-density plasma and processing aworkpiece with the generated neutral particle beam.

1. A neutral particle beam processing apparatus comprising: a workpieceholder for holding a workpiece; a plasma generator for generating aplasma in a vacuum chamber; an orifice electrode disposed between saidworkpiece holder and said plasma generator, said orifice electrodehaving orifices defined therein; a grid electrode disposed upstream ofsaid orifice electrode in said vacuum chamber; and a voltage applyingunit for applying a voltage between said orifice electrode and said gridelectrode via a dielectric to extract positive ions from the plasmagenerated by said plasma generator and pass the extracted positive ionsthrough said orifices in said orifice electrode.
 2. A neutral particlebeam processing apparatus according to claim 1, wherein said dielectriccomprises a dielectric film covering a surface of said orificeelectrode.
 3. A neutral particle beam processing apparatus comprising: aworkpiece holder for holding a workpiece; a plasma generator forgenerating a plasma in a vacuum chamber; an orifice electrode disposedbetween said workpiece holder and said plasma generator, said orificeelectrode having orifices defined therein; a grid electrode disposedupstream of said orifice electrode in said vacuum chamber; and a voltageapplying unit for applying a high-frequency voltage between said orificeelectrode and said grid electrode via a dielectric to generate a plasmabetween said orifice electrode and said grid electrode and to extractpositive ions from the generated plasma and pass the extracted positiveions through said orifices in said orifice electrode.
 4. A neutralparticle beam processing apparatus according to claim 3, wherein saiddielectric comprises a dielectric film covering a surface of saidorifice electrode.